The structural design, chemical synthesis, and modification of molecules important to reproductive and developmental biology are the focus of this study. A. Broad spectrum anti-microbial substances (Magainins) isolated from skin of Xenopus laevis have been purifed to homogeneity by reverse-phase high performance liquid chromatography. Amino acid sequence analyses by Edman degration and carboxypeptidase Y digestion have revealed two sequences, magainin I and II which differ in two substitutions shown in parentheses for II: G-I-G-K- F-L-H-S-A-G(K)K-F-G-K-A-F-V-G-E-I-M-K(N)-S. These sequences have been confirmed by both chemical synthesis and cDNA sequence analyses. Circular dichroism studies indicate that margainin peptides do not form alpha-helices in aqueous buffers. However, magainin I and II display 24% and 26% alpha-helical conformation in lipophilic solution (49% trifluoroethanol), respectively. These results indicate that the peptides are amphiphilic in structure which suggests that the lytic action of magainins may stem from a highly selective penetration into bilayers of microorganisms. B. A peptide comprising the last 37 residues of human chorionic gonadotropin beta-subunit has been synthesized and purified. Through the thiol function of Cys2, the peptide was coupled to a m-maleimidobenzoylated epsilon-amino groups of Keyhole Limpet hemocyanin. This two-step conjugation approach yields a conjugate which contains 2:1 peptide to protein ratio (by weight) and permits the maximal exposure of antigenic sites.